The present invention relates in general to a system for testing and calibrating optical detectors, such as for example, hydrogen fire detectors.
Hydrogen fires present a significant danger during rocket launch preparations at the Kennedy Space Center. These types of fires are particularly hazardous if they occur during daylight hours because hydrogen burns with a flame that is virtually invisible to the naked eye. As a result of this potential hazard, the Kennedy Space Center has installed groups of special detectors at each launch pad which can detect the presence of a hydrogen fire. These detectors are specifically shortwave ultraviolet (UV) detectors which utilize a Hamamatsu ultraviolet detector tube to indicate the presence of radiation in the optical wavelength range from 180 nm to 240 nm. This spectral window is unique for within it, a hydrogen fire emits a small amount of radiation, while incandescent lamps and the sun emit no significant radiation, and the air is transmissive. Consequently, this spectral region is very favorable for monitoring hydrogen fires in air with a minimum possibility of false alarms.
Each launch pad utilizes about 60 hydrogen fire detectors in one of three configurations referred to as (-1), (-2) and (-3). A (-2) unit has an unmodified configuration designed to alarm off of a standard hydrogen fire (defined as the fire produced by burning H.sub.2 flowing at 5 SLPM through a 1/16" orifice) at a distance of 24 feet. A (-1) unit is a (-2) unit with a screen mesh added to reduce sensitivity to the point where the unit will alarm off of a standard hydrogen fire at 15 feet. A (-3) unit has modified electronics added to increase the sensitivity such that it will alarm at a distance of 54 feet from a standard hydrogen fire.
Before the fire detectors are installed at the launch pad, they must be tested and calibrated to insure that they work properly. In the past, the calibration procedure has been performed in a laboratory by exposing the detectors to an actual hydrogen flame. However, recent hydrogen fire safety restrictions have prevented the calibration laboratory from being able to calibrate the detectors using an actual hydrogen flame. Also, the same restrictions prevent operations personnel from checking the performance of the units in the field, and have made it difficult for the NASA Sensors and Transducer Laboratory to do the same. Consequently, it has become almost impossible to determine whether a hydrogen fire detector meets specifications by performing tests on KSC property. This has created a need for a fire detector calibration and testing device which can accurately test the operation of a hydrogen fire detector without use of an actual hydrogen flame.